A variable capacitor (300) comprises cells (200, 400) that have an RF electrode (202, 402) coupled to a bond pad (30). Each cell comprises a plurality of MEMS devices (100) the capacitance of which can be changed by means of a movable electrode. The MEMS devices are placed in a sealed cavity of the cell and are arranged next to each other along the length of the RF electrode of the cell. The RF electrode of each cell can be trimmed so as to obtain an RF line (402) and a further ground electrode (404) and so as to scale the RF capacitance of the cell without impacting the mechanical performance of the MEMS cells. Each cell has the same control capacitance irrespective of the RF capacitance. This allows each cell to use the same isolation resistor required for RF operation and thus each cell has the same parasitic capacitance. This allows the CMOS control circuit to be optimized and the dynamic performance of the cells to be matched.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A variable capacitor, comprising: a substrate; one or more bond pads disposed over the substrate; a first cell disposed over the substrate and coupled to the one or more bond pads, the first cell having a first end and a second end and comprising: an RF electrode coupled to the one or more bond pads and the first end of the first cell; a plurality of MEMS devices disposed over the RF electrode, each MEMS device having a first end and a second end and each MEMS device disposed over the RF electrode; and one or more ground electrodes coupled to the first end and the second end of each MEMS device and to the second end of the first cell; and a second cell disposed over the substrate and coupled to the one or more bond pads, the second cell having a first end and a second end and comprising: an RF electrode coupled to the one or more bond pads; a plurality of MEMS devices disposed over the RF electrode, each MEMS device having a first end and a second end and less than all of the total MEMS devices in the second cell are disposed over the RF electrode; and one or more ground electrodes coupled to the first end and the second end of each MEMS device and to the second end of the first cell.
2. The variable capacitor of claim 1 , wherein the second cell additionally comprises a pull-in electrode having a length that is greater than the RF electrode of the second cell.
3. The variable capacitor of claim 1 , wherein the second cell further comprises a ground electrode disposed adjacent the RF electrode.
4. The variable capacitor of claim 3 , wherein RF electrode is spaced from the ground electrode by a distance of between about 1 micrometers to about 10 micrometers.
5. The variable capacitor of claim 1 , wherein the first cell and the second cell each have a different capacitance.
6. The variable capacitor of claim 5 , wherein the second cell additionally comprises a pull-in electrode having a length that is greater than the RF electrode of the second cell.
7. The variable capacitor of claim 1 , wherein each cell is a sealed cavity that includes the plurality of MEMS devices collectively enclosed within the sealed cavity.
8. A variable capacitor, comprising: a substrate; one or more bond pads disposed over the substrate; a first cell disposed over the substrate and coupled to the one or more bond pads, the first cell having a first capacitance, a first end and a second end and comprising: an RF electrode coupled to the one or more bond pads and the first end of the first cell; a first plurality of MEMS devices disposed over the RF electrode, each MEMS device having a first end and a second end; and one or more ground electrodes coupled to the first end and the second end of each MEMS device and to the second end of the first cell; and a second cell disposed over the substrate and coupled to the one or more bond pads, the second cell having a second capacitance that is less than the first capacitance, a first end and a second end and comprising: an RF electrode coupled to the one or more bond pads; a second plurality of MEMS devices disposed over the RF electrode, each MEMS device having a first end and a second end, the second plurality of MEMS devices is equal to the first plurality; and one or more ground electrodes coupled to the first end and the second end of each MEMS device and to the second end of the first cell.
9. The variable capacitor of claim 8 , wherein the second cell additionally comprises a pull-in electrode having a length that is greater than the RF electrode of the second cell.
10. The variable capacitor of claim 8 , wherein the second cell further comprises a ground electrode disposed adjacent the RF electrode.
11. The variable capacitor of claim 10 , wherein RF electrode is spaced from the ground electrode by a distance of between about 1 micrometers to about 10 micrometers.
12. The variable capacitor of claim 11 , wherein each cell is a sealed cavity that includes the plurality of MEMS devices collectively enclosed within the sealed cavity.
13. The variable capacitor of claim 12 , wherein the second cell additionally comprises a pull-in electrode having a length that is greater than the RF electrode of the second cell.
14. The variable capacitor of claim 8 , wherein each cell is a sealed cavity that includes the plurality of MEMS devices collectively enclosed within the sealed cavity.
15. A variable capacitor, comprising: a substrate; one or more bond pads disposed over the substrate; a first cell disposed over the substrate and coupled to the one or more bond pads, the first cell having a first end, a second end, a first volume and comprising: an RF electrode coupled to the one or more bond pads and the first end of the first cell, the RF electrode having a first length; a plurality of MEMS devices disposed over the RF electrode, each MEMS device having a first end and a second end; and one or more ground electrodes coupled to the first end and the second end of each MEMS device and to the second end of the first cell; and a second cell disposed over the substrate and coupled to the one or more bond pads, the second cell having a first end, a second end, and a second volume substantially equal to the first volume and comprising: an RF electrode coupled to the one or more bond pads, the RF electrode having a second length that is less than the first length; a plurality of MEMS devices disposed over the RF electrode, each MEMS device having a first end and a second end, and at least one MEMS device disposed in a section of the second volume where the RF electrode is not disposed; and one or more ground electrodes coupled to the first end and the second end of each MEMS device and to the second end of the first cell.
16. The variable capacitor of claim 15 , wherein the second cell additionally comprises a pull-in electrode having a third length that is greater than the second length.
17. The variable capacitor of claim 16 , wherein the first cell additionally comprises a pull-in electrode having a fourth length that is equal to the second length.
18. The variable capacitor of claim 15 , wherein the second cell further comprises a ground electrode disposed adjacent the RF electrode.
19. The variable capacitor of claim 18 , wherein RF electrode is spaced from the ground electrode by a distance of between about 1 micrometers to about 10 micrometers.
20. The variable capacitor of claim 15 , wherein each cell is a sealed cavity that includes the plurality of MEMS devices collectively enclosed within the sealed cavity.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
August 7, 2013
September 13, 2016
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